Doing it yourself qualifies as "a single expert is still a single point of failure". A single vendor at least has some levels of staffing and redundancy that I nor my company can match.
Do you really need to spend the time (and maybe money) for a second host just because your current one might go down for an hour? There's probably a point at which you might rightly consider it, but I doubt many people are legitimately at that threshold. Especially given I don't even remember the last time Netlify had this issue.
When did I ever say most people have this issue? Of course most don’t. But there are many that do: an hour of lost sales a few times a year can easily justify the very easy efforts of running two CDNs. You’re vastly overestimating the cost (human and financial).
In my business, being down for an hour would be a very big deal.
The sad thing here is that front end (or stateless for that matter) is actually fairly easy to run across two CDNs